Thermal ink jet printers apply ink to a print medium by ejecting small droplets of ink from an array of nozzles located in the printhead of a print cartridge. An array of thin-film resistors on an integrated circuit on the printhead selectively generates heat as current is passed through the resistors. The heat causes ink contained within an ink reservoir adjacent to the resistors to boil and be ejected from the array of nozzles associated with the resistor array. A printer controller determines which resistors will be "fired" and the proper firing sequence so that the desired pattern of dots is printed on the medium to form an image.
Conventional ink jet printers accommodate replaceable print cartridges containing either multiple colors of ink or a single color of ink. When the print cartridge is changed, information identifying the type of cartridge installed must be given to the printer so that the printer will function properly with the cartridge. User intervention is conventionally used to identify to the printer controller the type of cartridge installed.
In order to reduce the cost and complexity of print cartridge manufacturing processes, it is desirable for all cartridges used with a printer to be constructed with a similar configuration regardless of the type of cartridge or color of ink the cartridge contains. Thus it is desirable to maintain substantial overall uniformity of the cartridge shapes and sizes so that a single cartridge design can be used for multiple purposes. However, maintaining a uniform cartridge design makes it more difficult to easily identify the contents of the cartridge or the particular cartridge being used.
An object of the invention is to provide a relatively simple and inexpensive apparatus for encoding information on a replaceable print cartridge.
Another object of the invention is to provide cartridge-specific information, such as ink color and type of cartridge, directly on the cartridge in a manner that is detectable by the printer controller so that the controller may be automatically adjusted without the need for user intervention.
A further object of the invention is to provide a cartridge encoding system which can be configured for a wide variety of cartridge types.